基于叠前弹性阻抗反演的古近系流体识别

Paleogene fluid identification based on pre-stack elastic impedance inversion

对于地震-地质条件十分复杂的古近系地层,Gassmann流体因子相对常规岩石物理参数通常具有更好的油气检测能力.然而,在由叠前反演结果计算流体因子的过程中往往会引入新的中间误差.为此,首先基于饱和流体多孔弹性介质理论推导了Zoeppritz方程的Russell近似表达式,该方程将纵波反射系数表示为流体因子f、剪切模量μ以及密度ρ的函数.进而结合叠前弹性阻抗反演理论,实现了流体因子f的直接计算.该方法兼顾了弹性阻抗反演算法较强的抗噪能力和流体因子较强的油气识别能力,同时有效避免了传统叠前反演方法在间接计算流体因子过程中产生的累积误差.将该方法应用于渤海油田锦州A构造古近系油气检测,研究结果表明,流体因子f反演结果能够有效识别并清晰刻画出研究区古近系东营组强、中、弱等不同振幅对应的油气层.研究成果指导该区井位部署并得到钻探结果证实,为渤海油田古近系油气勘探开发提供了有力的技术支撑.

For the Paleogene strata with complicated seismicgeological conditions, Gassmann fluid factor usually has better hydrocarbon detection capability than conventional rock physics parameters. However,new intermediate errors are often introduced in the calculation of fluid factors from pre-stack inversion results.Therefore,the Russell approximation of Zoeppritz equation is firstly deduced based on saturated fluid porous elastic medium theory,which expresses the P-wave reflection coefficient as the function of fluid factor f,shear modulus μ and density ρ. Then the direct computation of fluid factor f is realized in combination with pre-stack elastic impedance inversion. This method gives consideration to favorable anti-noise ability of elastic impedance inversion algorithm and great hydrocarbon detection capability of the fluid factor,and the cumulative error caused by indirect calculation of fluid factor by traditional pre-stack inversion method is effectively avoided. The method is then applied to Paleogene hydrocarbon detection in Jinzhou-A structure in Bohai Oilfield. Result shows that reservoirs with different amplitudes in Dongying Formation can be effectively identified and characterized by the inversion result of fluid factor f.Research results are used for well deployment within this area and are confirmed by the drilling outcome,which provides favorable technical support for hydrocarbon exploration of Paleogene within this area.